With the development of the laser technology, there is a demand for laser radiation with different wavelengths in applications. However, the frequently used laser sources can only emit laser lights with fixed frequencies. Thus, frequency conversions turn to be absolutely necessary. By utilizing the nonlinear effects of nonlinear optical crystals, i.e. the second harmonic generation (SHG), sum-frequency generation (SFG), difference-frequency generation (DFG) and parametric amplification, the frequency of the input laser sources can be converted. In the visible and ultraviolet range, the current widely used frequency-converting crystals are KTP (KTiOPO4), KDP (KH2 PO4), BBO (BaB2O4), LBO (LiB3O5), etc. However, the former two are not suitable for high-power laser applications due to their low anti-radiation damage capabilities. In addition, both of them are not suitable for applications in the UV region because KTP shows absorption in the UV region and KDP has a small birefringence. BBO has a photorefractive effect and a decrease of the effective frequency-doubling coefficient in the UV region. LBO has a relatively small natural birefringence so that it can not achieve the UV output of higher than third-harmonic generation of Nd:YAG. Therefore, it is necessary to supplement crystals with better properties. At present, there are two crystals which can be used as such candidates: CLBO (CsLiB6O10) and CBO (CsB3O5). CLBO can achieve the fourth-harmonic generation of Nd:YAG laser and obtain high-power coherent light output at 266 nm. However, the crystal has a drawback in that it is hygroscopic in ambient environment and thus causing cracking so that it needs to be kept at a temperature above 100° C., leading to the inconvenience in its applications. CBO has a large effective nonlinear coefficient in third-harmonic generation, which is favorable for the high-power laser output at 355 nm. Unfortunately, it also encounters the same problems, such as hygroscopy, a small effective birefringence, etc.